While the previous blast was initially being investigated as a suspicious death, it is now being viewed as a homicide and took place 12 miles from where Monday’s incident occured.

According to Manley, investigators believe the attacks are related, as in both cases, the packages were left overnight on the victims' doorsteps and were not mailed or sent by a delivery service.

He further added that the U.S. Postal Service doesn't have a record of delivering the package to the East Austin home where Monday's explosion occurred.

Further, private carriers like UPS and FedEx have also confirmed they had no record of the package.

Manley said, "There are similarities that we cannot rule out that these two items are, in fact, related,” adding that investigators haven't determined a motive for the attacks, but it is possible that the victims could have been targeted because they are black.

He said, "We don't know what the motive behind these may be. We do know that both of the homes that were the recipients of these packages belong to African-Americans, so we cannot rule out that hate crime is at the core of this. But we're not saying that that's the cause as well."

Meanwhile, Special Agent Michelle Lee, a San Antonio-based spokesman for the FBI, said the agency "responded to both events" and was assisting Austin police which were taking the lead on the investigation.

Lee added that the Bureau of Alcohol, Tobacco, Firearms and Explosives was taking the lead on the federal investigation.